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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

I have thought many times on the cheap way out for a smoke machine that one could afford and would do the job required of it. Today I have seen just such a machine in action.
The machine I speak of is not one from a Automotive parts supplier, the machine that I saw in action comes from Spencer Gifts and it's used for the smoke effects around Halloween.
Caught a buddy that has a import repair shop using this 30 buck gadget and he told me he had been using it for years--does the job and works just great. I'm headed to Spencers
what a great idea.

Access the throttle plate and wedge it open, then replace the air intake hose. Remove the air filter. Seal off the air inlet to the air box with a plastic bag and rubber band. Fill with water, add dry ice, and close the air box. The intake will then fill with CO2 / water vapor 'fog'. Should be detectable wherever it's leaking.

That seems to be the same setup I referenced. The problem, of course, is actually building it and generating the few PSI (4 psi?) of smoke that is needed.

Sry, B. I dint read your post

Yea, I believe it should be less than 4psi since greater the pressure, the bigger chance of you blowing out the seals. My only problem with the Halloween smoke machine is that the vapor that comes out of it is really hot so i cant just simply put a rubber hose on the tip and call it a day...

I've googled smoke machines and realized the similarities & differences - and I came up with my own idea for a smoke machine that is the simplest of them all (if it works).

There are three and two hole designs; but I have an idea for a one hole design.

These are the typical three holes for a smoke machine:
#1: You need an exit for the smoke to be piped to your manifold (usually connected after the MAF to the air intake)
#2: All seem to have a mechanism to generate pressure (about 2psi to 4psi)
#3: Many have a heating mechanism to generate smoke (the cleaner, the better, for the sake of your components)

The typical 3-hole smoke machine:

Is a metal container (typically a $1 paint can)

Which is filled with smoke fluid (typically a glycol)

Which is heated by a heating element (typically a $10 glow plug)

Which is forced out by air pressure (typically from a compressor or fan)

The typical 2-hole smoke machine:

Does away with the heating element (typically using a diesel soaked rag, burned and capped)

Some use dry ice for the smoke instead of the smothered soaked rag

My idea for the world's simplest single-hole smoke machine:

Creates both its smoke & pressure from the same action!

All it needs is a hole for the smoke to exit the container

I bought some of the parts already - and will attempt to create one or more of the smoke machines above to diagnose a persistent vacuum leak.

I heartily recommend a smoke machine for anyone tracking down a variety of lean condition misfire codes.

Here, by way of example, is how I solved my long standing lean condition misfire codes ...

a) I first replaced all the rubber tubes/hoses/pipes/plugs I could easily get to in the engine bay ... which immediately helped somewhat lessen the frequency of the lean-condition misfire codes ...
- Where in the USA to get new vacuum tubing & vacuum caps (1) & what SAE sizes to get for all the metric M54 engine vacuum tubes, hoses, pipes, and caps (1) & correcting the F-connector errors in the realoem diagrams (1) & finding the ends of hard-to-locate vacuum tubes (1) & sorely needed clarification on how the M54 CCV vacuum port works on the M52 CCV valve connection to the fuel pressure regulator connection (1)

b) I then ran a smoke test ...
- How to make or buy your own smoke machine (1)

d) I also unclogged the dipstick guide tube which was clogged solid (and perhaps was a reason for the CCV vent hose leak) ...
- How to test, clean, & redesign the original BMW dipstick guide tube to prevent CCV vent clogs (1)

e) Lastly, I replaced the rubber boot which is connected to the ICV & TCV.

Those simple steps resolved my lean condition misfires!

BTW, while I rarely solve problems by replacing components without learning how to test them, I concur that one way to solve perplexing lean condition misfires, at this age of our bimmers, is to simply replace every vacuum-related rubber hose/tube/pipe/boot/cap/gasket in the engine bay.

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Please read the suggested threads, where the best always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need

Slightly off topic, has anyone tried an air compressor and soapy water? I use this method to find vacuum leaks in my intercooler piping. I use 6-8 psi of air pressure and a mix of Dawn and water. You can usually hear the leak, but a bubbly visual is always helpful. Similar to finding a leak in a tire.